In humans and other animals, iron is essential for the implementation and maintenance of many vital cellular functions and biosynthetic processes, including oxygen transport, aerobic cellular activity, intracellular electron transport, and integral enzymatic reactions within body tissue. Iron deficiency is the most common nutritional deficiency worldwide, affecting 30 million people in both developed and developing countries. Iron deficiency has many repercussions including diminishing growth and learning in children.
The majority of stored iron in body tissues is contained in ferritin. Ferritin is an intracellular, protein-iron complex, formed from self-assembling subunits. The protein cage can reversibly form iron into a caged biomineral, Fe2O3.H2O, in plants, animals, and bacteria. Iron oxy-biominerals inside the protein nanocages are iron concentrates for protein synthesis, and Fe(II)/oxygen/peroxide traps (Fenton chemistry reactants) for antioxidant protection. The iron contained in ferritin is concentrated 100 billion times above the solubility of ferric ion in a nontoxic, accessible form. Ferritin protein subunits, four α-helix bundles, contain a catalytic center that converts two Fe(II) atoms to an Fe(III)-oxo bridged dimer intermediate in mineralization. The two classes of ferritins are: i) maxi-ferritins, 24-polypeptide, 4-bundle subunit assemblies found in animals, plants, and bacteria; and ii) mini-ferritins (also called Dps proteins), 12-polypeptide, 4-bundle subunit assemblies in archaea and bacteria.
In animals, ferritin is mainly present in tissues, especially in the liver, kidney, spleen and bone marrow erythroid cells where it serves as an iron reserve for the production of hemoglobin. A small fraction of ferritin is in the serum and contributes little to overall iron storage, but is used clinically as a reporter of iron levels in an animal. Ferritins occur in animals as approximately 25 distinct isoforms depending on their proportions of the two primary subtypes of ferritins, H or L. These distinct subtypes differ in their tissue distribution, rates and mechanisms of iron oxidation, core formation and physiological iron turnover.
Ferritin derived from plants and animals can be used as a dietary source for humans and other animals. Ferritin, which survives digestion largely intact, is more efficiently absorbed by the intestine than any other dietary iron source or iron supplement, because of the large amount of iron per ferritin molecule. Ferritin also survives treatment with high heat. The ferritin protein makes ferritin iron a naturally enteric coated, slow release, efficiently absorbed iron source. As such, ferritin can used to supplement iron in animals in need of increased iron in their diet.
Currently, there is a need for methods to isolate plant and animal ferritin from a low-cost, readily available source, which can be administered to a subject in an amount to treat an iron deficiency disorder or prevent iron deficiency. There is also a need for methods to determine the amount of iron derived from animal and plant ferritin.